In an electrophotographic apparatus, the photoreceptor is used in a series of electrophotographic processes; that is, in repetitive processes of primary charging, forming of an electrostatic latent image by image exposure, development of toner charged in reverse polarity of the electrostatic image, transfer of the toner image on plain paper, removal of residual toner on the drum by a cleaning device, and removal of electric charge on the drum by intense exposure.
In these processes, the talc and residual toner of the paper on the photoconductor drum are usually removed by using a cleaning roller or cleaning blade.
The required characteristics of the blade are to remove the toner efficiently from the photoconductor drum and to prevent the removed toner from depositing on the blade.
As the blade material, polyurethane rubber is generally used because it is excellent in wear resistance.
In the fixing process, the toner is permanently adhered to the paper by heat or pressure. The fixing process is the step for determining the final image. When the adhesion of the toner and the roller surface becomes stronger than the aggregation of toner particles, the toner deposits on the roller, which causes background noise on the copy. That is, the toner is stuck on the white background. To prevent this, the roller surface is coated with polytetrafluoroethylene to weaken toner adhesion.
In the fixing process, in order to improve the paper offset property, the separation pawl is used. To prevent the toner from sticking to the separation pawl, the surface of the separation pawl made of polyamide is coated with a resin containing fluorine, and is baked (Japanese Patent Publication Sho. 61-23554).
In the corona charging process, the photoconductor surface is uniformly charged by corona discharge by means of a corona wire. The corona wire is usually made of gold-coated tungsten wire.
Also in the fixing process, the photoconductor surface is uniformly charged by corona discharge by means of a charger. The corona grid is generally made of stainless steel.
If an attempt is made to remove the toner in this method, however, a slight amount of paper talc and toner is not removed but is left on the photoconductor drum. When the image is repeatedly formed, white blanks or black spots may appear on the image and lower the image quality. Or if the cleaning roller or cleaning blade is applied by force in order to remove toner, the electric charge of the surface layer of the photoconductor is charged which lowers the durability.
Moreover, if fixed repeatedly by using a fixing roller, the toner is deposited on the roller surface, and black spots appear on the image if the images are formed repeatedly, and the image quality drops. This is because, due to repeated fixings, the Teflon ("Teflon" is the trademark for polytetrafluoroethylene) coated surface is injured or is partly torn, and the toner parting property is lowered.
In the conventional separation pawl, if used repeatedly at 200.degree. C. or more, the fluorine-containing resin film may be injured or partly torn, and the toner parting property is lowered which impairs the image quality.
By repeating the charging process in the electrophotographic apparatus using a charger, the toner deposits on the corona wire, and when the images are formed repeatedly, image disturbance or black spots may appear on the image which lowers the image quality. This is because the corona wire is not provided with the toner parting property.
Also by repeating the charging process in the electrophotographic apparatus using such charger, the toner deposits on the corona grid, and when images are formed repeatedly, image disturbances or black spots may appear on the image which lowers the image quality. This is because the corona grid is not provided with the toner parting property.